Class: R6502::Cpu

Inherits:
Object
  • Object
show all
Defined in:
lib/r6502/instr_table.rb,
lib/r6502/cpu_execution.rb,
lib/r6502/cpu_instructions.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(mem) ⇒ Cpu

Returns a new instance of Cpu.



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# File 'lib/r6502/cpu_execution.rb', line 5

def initialize(mem)
  @mem = mem
  @pc = @mem.get_word(0xfffc)
  @s  = 0xff
  @x  = 0x00
  @y  = 0x00
  @a  = 0x00
  @c  = 0
  @z  = 0
  @i  = 0
  @d  = 0
  @b  = 0
  @v  = 0
  @n  = 0
end

Instance Attribute Details

#a ⇒ Object

Returns the value of attribute a.



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# File 'lib/r6502/cpu_execution.rb', line 3

def a
  @a
end

#b ⇒ Object

Returns the value of attribute b.



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# File 'lib/r6502/cpu_execution.rb', line 4

def b
  @b
end

#c ⇒ Object

Returns the value of attribute c.



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# File 'lib/r6502/cpu_execution.rb', line 4

def c
  @c
end

#d ⇒ Object

Returns the value of attribute d.



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# File 'lib/r6502/cpu_execution.rb', line 4

def d
  @d
end

#i ⇒ Object

Returns the value of attribute i.



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# File 'lib/r6502/cpu_execution.rb', line 4

def i
  @i
end

#mem ⇒ Object

Returns the value of attribute mem.



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# File 'lib/r6502/cpu_execution.rb', line 3

def mem
  @mem
end

#n ⇒ Object

Returns the value of attribute n.



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# File 'lib/r6502/cpu_execution.rb', line 4

def n
  @n
end

#pc ⇒ Object

Returns the value of attribute pc.



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# File 'lib/r6502/cpu_execution.rb', line 3

def pc
  @pc
end

#s ⇒ Object

Returns the value of attribute s.



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# File 'lib/r6502/cpu_execution.rb', line 3

def s
  @s
end

#v ⇒ Object

Returns the value of attribute v.



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# File 'lib/r6502/cpu_execution.rb', line 4

def v
  @v
end

#x ⇒ Object

Returns the value of attribute x.



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# File 'lib/r6502/cpu_execution.rb', line 3

def x
  @x
end

#y ⇒ Object

Returns the value of attribute y.



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# File 'lib/r6502/cpu_execution.rb', line 3

def y
  @y
end

#z ⇒ Object

Returns the value of attribute z.



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# File 'lib/r6502/cpu_execution.rb', line 4

def z
  @z
end

Instance Method Details

#adc(arg, mode) ⇒ Object

add with carry



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# File 'lib/r6502/cpu_instructions.rb', line 4

def adc(arg, mode)
  x = @a
  y = mode == :imm ? arg : @mem.get(arg)
  if @d == 0 #normal binary mode
    r = x + y + @c
    @a = 0xff & r
    @v = (((0x7f&x) + (0x7f&y) + @c)>>7) ^ ((x + y + @c)>>8)
    @z = (r&0xff).zero? ? 1 : 0
    @c = r > 255 ? 1 : 0
    @n = (0x80&r)>>7
  else #BCD mode
    ones = (0xf&x) + (0xf&y)
    tens = ((0xf0&x)>>4) + ((0xf0&y)>>4)
    r0 = ones + 10*tens + @c
    @c = r0 > 99 ? 1 : 0
    r = r0 % 100
    @z = r.zero? ? 1 : 0
    @a = r + 6*((r/10).floor)
    @n = (0x80&@a)>>7
  end
  inc_pc_by_mode(mode)
end

#and(arg, mode) ⇒ Object

logical and



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# File 'lib/r6502/cpu_instructions.rb', line 51

def and(arg, mode)
  case mode
  when :imm
    @a = @a & arg
  else
    @a = @a & @mem.get(arg)
  end
  @z = @a.zero? ? 1 : 0
  @n = @a>>7
  inc_pc_by_mode(mode)
end

#asl(arg, mode) ⇒ Object

shift left



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# File 'lib/r6502/cpu_instructions.rb', line 63

def asl(arg, mode)
  case mode
  when :acc
    r = @a<<1
    @a = r&0xff
    @z = @a.zero? ? 1 : 0
    @n = @a>>7
    @c = r > 0xff ? 1 : 0
  else
    r = @mem.get(arg)<<1
    @mem.set( arg, r&0xff )
    @z = r.zero? ? 1 : 0
    @n = r>>7
    @c = r > 0xff ? 1 : 0
  end
  inc_pc_by_mode(mode)
end

#bcc(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 236

def bcc(arg, mode)
  inc_pc_by_mode(:rel)
  @pc += arg if @c == 0
end

#bcs(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 240

def bcs(arg, mode)
  inc_pc_by_mode(:rel)
  @pc += arg if @c == 1
end

#beq(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 244

def beq(arg, mode)
  inc_pc_by_mode(:rel)
  @pc += arg if @z == 1
end

#bit(arg, mode) ⇒ Object

logical and (result discarded)



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# File 'lib/r6502/cpu_instructions.rb', line 81

def bit(arg, mode)
  m = @mem.get( arg )
  a = @a
  result = a & m
  @z = result.zero? ? 1 : 0
  @v = (m & 0x40)>>6
  @n = (m & 0x80)>>7
  inc_pc_by_mode(mode)
end

#bmi(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 248

def bmi(arg, mode)
  inc_pc_by_mode(:rel)
  @pc += arg if @n == 1
end

#bne(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 252

def bne(arg, mode)
  inc_pc_by_mode(:rel)
  @pc += arg if @z == 0
end

#bpl(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 256

def bpl(arg, mode)
  inc_pc_by_mode(:rel)
  @pc += arg if @n == 0
end

#brk(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 457

def brk(arg, mode)
  @mem.set(0x0100 + @s, @pc>>8)
  @s -= 1
  @mem.set(0x0100 + @s, (0xff&@pc))
  @s -= 1
  val =            @n #bit 7
  val = (val<<1) + @v #bit 6
  val = (val<<1) +  1 #bit 5
  val = (val<<1) +  1 #bit 4 break flag
  val = (val<<1) + @d #bit 3
  val = (val<<1) + @i #bit 2
  val = (val<<1) + @z #bit 1
  val = (val<<1) + @c #bit 0
  @mem.set(0x0100 + @s, val)
  @s -= 1

  lo = @mem.get(0xfffe)
  hi = @mem.get(0xffff)
  @pc = (hi<<8) + lo
end

#bvc(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 260

def bvc(arg, mode)
  inc_pc_by_mode(:rel)
  @pc += arg if @v == 0
end

#bvs(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 264

def bvs(arg, mode)
  inc_pc_by_mode(:rel)
  @pc += arg if @v == 1
end

#clc(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 268

def clc(arg, mode)
  @c = 0
  inc_pc_by_mode(mode)
end

#cld(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 272

def cld(arg, mode)
  @d = 0
  inc_pc_by_mode(mode)
end

#cli(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 276

def cli(arg, mode)
  @i = 0
  inc_pc_by_mode(mode)
end

#clv(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 280

def clv(arg, mode)
  @v = 0
  inc_pc_by_mode(mode)
end

#cmp(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 284

def cmp(arg, mode)
  case mode
  when :imm
    result = @a - arg
    @c = result >= 0 ? 1 : 0
    @z = result == 0 ? 1 : 0
    @n = (0xff&result)>>7
  else
    m = @mem.get( arg )
    result = @a - m
    @c = result >= 0 ? 1 : 0
    @z = result == 0 ? 1 : 0
    @n = (0xff&result)>>7
  end
  inc_pc_by_mode(mode)
end

#cpx(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 300

def cpx(arg, mode)
  case mode
  when :imm
    result = @x - arg
    @c = result >= 0 ? 1 : 0
    @z = result == 0 ? 1 : 0
    @n = (0xff&result)>>7
  else
    m = @mem.get( arg )
    result = @x - m
    @c = result >= 0 ? 1 : 0
    @z = result == 0 ? 1 : 0
    @n = (0xff&result)>>7
  end
  inc_pc_by_mode(mode)
end

#cpy(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 316

def cpy(arg, mode)
  case mode
  when :imm
    result = @y - arg
    @c = result >= 0 ? 1 : 0
    @z = result == 0 ? 1 : 0
    @n = (0xff&result)>>7
  else
    m = @mem.get( arg )
    result = @y - m
    @c = result >= 0 ? 1 : 0
    @z = result == 0 ? 1 : 0
    @n = (0xff&result)>>7
  end
  inc_pc_by_mode(mode)
end

#dec(arg, mode) ⇒ Object

decrement (memory)



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# File 'lib/r6502/cpu_instructions.rb', line 91

def dec(arg, mode)
  r = @mem.get(arg) - 1
  @mem.set( arg, r&0xff )
  @z = r.zero? ? 1 : 0
  @n = (r&0x80)>>7
  inc_pc_by_mode(mode)
end

#decode_arg(mode, sec_word, thd_word) ⇒ Object 



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# File 'lib/r6502/cpu_execution.rb', line 29

def decode_arg(mode, sec_word, thd_word)
  case mode
  when :imp
      nil
  when :acc
      nil
  when :imm
    sec_word
  when :zp
    sec_word
  when :zpx
    sec_word + @x
  when :zpy
    sec_word + @y
  when :rel
    sec_word <= 127 ? sec_word : sec_word - 256
  when :abs
    (thd_word<<8) + sec_word
  when :absx
    (thd_word<<8) + sec_word + @x
  when :absy
    (thd_word<<8) + sec_word + @y
  when :ind
    lb = @mem.get( (thd_word<<8) + sec_word )
    hb = @mem.get( (thd_word<<8) + sec_word + 1 )
    (hb<<8) + lb
  when :indx
    lb = @mem.get( 0xff & (@x + sec_word) )
    hb = @mem.get( 0xff & (@x + sec_word) + 1 )
    @mem.get( (hb<<8) + lb )
  when :indy
    lb = @mem.get( 0xff & sec_word )
    hb = @mem.get( 0xff & sec_word + 1)
    addr = (hb<<8) + lb
    addr + @y
  end
end

#dex(arg, mode) ⇒ Object

decrement (x)



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# File 'lib/r6502/cpu_instructions.rb', line 99

def dex(arg, mode)
  r = @x - 1
  @x = r&0xff
  @z = @x.zero? ? 1 : 0
  @n = (@x&0x80)>>7
  inc_pc_by_mode(mode)
end

#dey(arg, mode) ⇒ Object

decrement (y)



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# File 'lib/r6502/cpu_instructions.rb', line 107

def dey(arg, mode)
  r = @y - 1
  @y = r&0xff
  @z = @y.zero? ? 1 : 0
  @n = (@y&0x80)>>7
  inc_pc_by_mode(mode)
end

#eor(arg, mode) ⇒ Object

exclusive or



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# File 'lib/r6502/cpu_instructions.rb', line 115

def eor(arg, mode)
  case mode
  when :imm
    @a = @a ^ arg
  else
    @a = @a ^ @mem.get(arg)
  end
  @z = @a.zero? ? 1 : 0
  @n = (@a&0x80)>>7
  inc_pc_by_mode(mode)
end

#inc(arg, mode) ⇒ Object

increment (memory)



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# File 'lib/r6502/cpu_instructions.rb', line 127

def inc(arg, mode)
  r = (@mem.get(arg) + 1)&0xff
  @mem.set( arg, r )
  @z = r.zero? ? 1 : 0
  @n = (r&0x80)>>7
  inc_pc_by_mode(mode)
end

#inc_pc_by_mode(mode) ⇒ Object 



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# File 'lib/r6502/cpu_execution.rb', line 66

def inc_pc_by_mode(mode)
  case mode
  when :imp
    @pc += 1
  when :acc
    @pc += 1
  when :imm
    @pc += 2
  when :zp
    @pc += 2
  when :zpx
    @pc += 2
  when :zpy
    @pc += 2
  when :abs
    @pc += 3
  when :absx
    @pc += 3
  when :absy
    @pc += 3
  when :indx
    @pc += 2
  when :indy
    @pc += 2
  when :rel
    @pc += 2
  when :ind #only used by jmp, which explicitly sets the pc,
    @pc += 3 #so hopefully this is never used here.
  end
end

#instr_mode(opcode) ⇒ Object 



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# File 'lib/r6502/instr_table.rb', line 3

def instr_mode(opcode)
#adc
  { 0x69 => [:adc, :imm],
    0x65 => [:adc, :zp],
    0x75 => [:adc, :zpx],
    0x6d => [:adc, :abs],
    0x7d => [:adc, :absx],
    0x79 => [:adc, :absy],
    0x61 => [:adc, :indx],
    0x71 => [:adc, :indy],
#and
    0x29 => [:and, :imm],
    0x25 => [:and, :zp],
    0x35 => [:and, :zpx],
    0x2d => [:and, :abs],
    0x3d => [:and, :absx],
    0x39 => [:and, :absy],
    0x21 => [:and, :indx],
    0x31 => [:and, :indy],
#asl
    0x0a => [:asl, :acc],
    0x06 => [:asl, :zp],
    0x16 => [:asl, :zpx],
    0x0e => [:asl, :abs],
    0x1e => [:asl, :absx],
#bit
    0x24 => [:bit, :zp],
    0x2c => [:bit, :abs],
#bpl
    0x10 => [:bpl, :rel],
#bmi
    0x30 => [:bmi, :rel],
#bvc
    0x50 => [:bvc, :rel],
#bvs
    0x70 => [:bvs, :rel],
#bcc
    0x90 => [:bcc, :rel],
#bcs
    0xb0 => [:bcs, :rel],
#bne
    0xd0 => [:bne, :rel],
#beq
    0xf0 => [:beq, :rel],
#brk
    0x00 => [:brk, :imp],
#cmp
    0xc9 => [:cmp, :imm],
    0xc5 => [:cmp, :zp],
    0xd5 => [:cmp, :zpx],
    0xcd => [:cmp, :abs],
    0xdd => [:cmp, :absx],
    0xd9 => [:cmp, :absy],
    0xc1 => [:cmp, :indx],
    0xd1 => [:cmp, :indy],
#cpx
    0xe0 => [:cpx, :imm],
    0xe4 => [:cpx, :zp],
    0xec => [:cpx, :abs],
#cpy
    0xc0 => [:cpy, :imm],
    0xc4 => [:cpy, :zp],
    0xcc => [:cpy, :abs],
#dec
    0xc6 => [:dec, :zp],
    0xd6 => [:dec, :zpx],
    0xce => [:dec, :abs],
    0xde => [:dec, :absx],
#eor
    0x49 => [:eor, :imm],
    0x45 => [:eor, :zp],
    0x55 => [:eor, :zpx],
    0x4d => [:eor, :abs],
    0x5d => [:eor, :absx],
    0x59 => [:eor, :absy],
    0x41 => [:eor, :indx],
    0x51 => [:eor, :indy],
#clc
    0x18 => [:clc, :imp],
#sec
    0x38 => [:sec, :imp],
#cli
    0x58 => [:cli, :imp],
#sei
    0x78 => [:sei, :imp],
#clv
    0xb8 => [:clv, :imp],
#cld
    0xd8 => [:cld, :imp],
#sed
    0xf8 => [:sed, :imp],
#inc
    0xe6 => [:inc, :zp],
    0xf6 => [:inc, :zpx],
    0xee => [:inc, :abs],
    0xfe => [:inc, :absx],
#jmp,
    0x4c => [:jmp, :abs],
    0x6c => [:jmp, :ind],
#jsr,
    0x20 => [:jsr, :abs],
#lda,
    0xa9 => [:lda, :imm],
    0xa5 => [:lda, :zp],
    0xb5 => [:lda, :zpx],
    0xad => [:lda, :abs],
    0xbd => [:lda, :absx],
    0xb9 => [:lda, :absy],
    0xa1 => [:lda, :indx],
    0xb1 => [:lda, :indy],
#ldx,
    0xa2 => [:ldx, :imm],
    0xa6 => [:ldx, :zp],
    0xb6 => [:ldx, :zpy],
    0xae => [:ldx, :abs],
    0xbe => [:ldx, :absy],
#ldy,
    0xa0 => [:ldy, :imm],
    0xa4 => [:ldy, :zp],
    0xb4 => [:ldy, :zpx],
    0xac => [:ldy, :abs],
    0xbc => [:ldy, :absx],
#lsr,
    0x4a => [:lsr, :acc],
    0x46 => [:lsr, :zp],
    0x56 => [:lsr, :zpx],
    0x4e => [:lsr, :abs],
    0x5e => [:lsr, :absx],
#nop,
    0xea => [:nop, :imp],
#ora,
    0x09 => [:ora, :imm],
    0x05 => [:ora, :zp],
    0x15 => [:ora, :zpx],
    0x0d => [:ora, :abs],
    0x1d => [:ora, :absx],
    0x19 => [:ora, :absy],
    0x01 => [:ora, :indx],
    0x11 => [:ora, :indy],
#tax,
    0xaa => [:tax, :imp],
#txa,
    0x8a => [:txa, :imp],
#dex,
    0xca => [:dex, :imp],
#inx,
    0xe8 => [:inx, :imp],
#tay,
    0xa8 => [:tay, :imp],
#tya,
    0x98 => [:tya, :imp],
#dey,
    0x88 => [:dey, :imp],
#iny,
    0xc8 => [:iny, :imp],
#rol,
    0x2a => [:rol, :acc],
    0x26 => [:rol, :zp],
    0x36 => [:rol, :zpx],
    0x2e => [:rol, :abs],
    0x3e => [:rol, :absx],
#ror,
    0x6a => [:ror, :acc],
    0x66 => [:ror, :zp],
    0x76 => [:ror, :zpx],
    0x6e => [:ror, :abs],
    0x7e => [:ror, :absx],
#rti,
    0x40 => [:rti, :imp],
#rts,
    0x60 => [:rts, :imp],
#sbc,
    0xe9 => [:sbc, :imm],
    0xe5 => [:sbc, :zp],
    0xf5 => [:sbc, :zpx],
    0xed => [:sbc, :abs],
    0xfd => [:sbc, :absx],
    0xf9 => [:sbc, :absy],
    0xe1 => [:sbc, :indx],
    0xf1 => [:sbc, :indy],
#sta,
    0x85 => [:sta, :zp],
    0x95 => [:sta, :zpx],
    0x8d => [:sta, :abs],
    0x9d => [:sta, :absx],
    0x99 => [:sta, :absy],
    0x81 => [:sta, :indx],
    0x91 => [:sta, :indy],
#txs,
    0x9a => [:txs, :imp],
#tsx,
    0xba => [:tsx, :imp],
#pha,
    0x48 => [:pha, :imp],
#pla,
    0x68 => [:pla, :imp],
#php,
    0x08 => [:php, :imp],
#plp,
    0x28 => [:plp, :imp],
#stx,
    0x86 => [:stx, :zp],
    0x96 => [:stx, :zpy],
    0x8e => [:stx, :abs],
#sty,
    0x84 => [:sty, :zp],
    0x94 => [:sty, :zpx],
    0x8c => [:sty, :abs] }[opcode]
end

#inx(arg, mode) ⇒ Object

increment (x)



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# File 'lib/r6502/cpu_instructions.rb', line 135

def inx(arg, mode)
  r = (@x + 1)&0xff
  @x = r
  @z = r.zero? ? 1 : 0
  @n = (r&0x80)>>7
  inc_pc_by_mode(mode)
end

#iny(arg, mode) ⇒ Object

increment (y)



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# File 'lib/r6502/cpu_instructions.rb', line 143

def iny(arg, mode)
  r = (@y + 1)&0xff
  @y = r
  @z = r.zero? ? 1 : 0
  @n = (r&0x80)>>7
  inc_pc_by_mode(mode)
end

#jmp(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 332

def jmp(arg, mode)
  @pc = arg
end

#jsr(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 496

def jsr( arg, mode )
  @mem.set(0x0100 + @s, (@pc+2)>>8)
  @s -= 1
  @mem.set(0x0100 + @s, 0xff&(@pc+2))
  @s -= 1
  @pc = arg
end

#lda(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 335

def lda(arg, mode)
  case mode
  when :imm
    @a = arg
  else
    @a = @mem.get( arg )
  end
  @z = @a.zero? ? 1 : 0
  @n = (0x80&@a)>>7
  inc_pc_by_mode(mode)
end

#ldx(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 346

def ldx(arg, mode)
  case mode
  when :imm
    @x = arg
  else
    @x = @mem.get( arg )
  end
  @z = @x.zero? ? 1 : 0
  @n = (0x80&@x)>>7
  inc_pc_by_mode(mode)
end

#ldy(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 357

def ldy(arg, mode)
  case mode
  when :imm
    @y = arg
  else
    @y = @mem.get( arg )
  end
  @z = @y.zero? ? 1 : 0
  @n = (0x80&@y)>>7
  inc_pc_by_mode(mode)
end

#lsr(arg, mode) ⇒ Object

shift right



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# File 'lib/r6502/cpu_instructions.rb', line 151

def lsr(arg, mode)
  case mode
  when :acc
    @c = 0x01&@a
    @a = @a>>1
    @z = @a.zero? ? 1 : 0
    @n = (@a&0x80)>>7 #bit 7 will always be zero, though
  else
    v = @mem.get(arg)
    @c = 0x01&v
    r = v>>1
    @z = r.zero? ? 1 : 0
    @n = (r&0x80)>>7
    @mem.set( arg, r )
  end
  inc_pc_by_mode(mode)
end

#nop(arg, mode) ⇒ Object

no operation



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# File 'lib/r6502/cpu_instructions.rb', line 221

def nop(arg, mode)
  inc_pc_by_mode(mode)
end

#ora(arg, mode) ⇒ Object

inclusive or



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# File 'lib/r6502/cpu_instructions.rb', line 169

def ora(arg, mode)
  case mode
  when :imm
    @a = @a | arg
  else
    @a = @a | @mem.get( arg )
  end
  @z = @a.zero? ? 1 : 0
  @n = (@a&0x80)>>7
  inc_pc_by_mode(mode)
end

#pha(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 368

def pha(arg, mode)
  addr = 0x0100 + (0xff & @s)
  @mem.set( addr, @a )
  @s -= 1
  inc_pc_by_mode(mode)
end

#php(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 382

def php(arg, mode)
  addr = 0x0100 + (0xff & @s)
  val =            @n #bit 7
  val = (val<<1) + @v #bit 6
  val = (val<<1) +  1 #bit 5, reserved
  val = (val<<1) +  1 #bit 4, break
  val = (val<<1) + @d #bit 3
  val = (val<<1) + @i #bit 2
  val = (val<<1) + @z #bit 1
  val = (val<<1) + @c #bit 0

  @mem.set( addr, val )
  @s -= 1
  inc_pc_by_mode(mode)
end

#pla(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 374

def pla(arg, mode)
  addr = 0x0100 + (0xff & (@s + 1))
  @a = @mem.get( addr )
  @s += 1
  @z = @a.zero? ? 1 : 0
  @n = (0x80&@a)>>7
  inc_pc_by_mode(mode)
end

#plp(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 397

def plp(arg, mode)
  addr = 0x0100 + (0xff & (@s + 1))
  val = @mem.get( addr )
  @c = 0x1 & val
  @z = 0x1 & (val>>1)
  @i = 0x1 & (val>>2)
  @d = 0x1 & (val>>3)
  @b = 0x1 & (val>>4)
  # bit 5
  @v = 0x1 & (val>>6)
  @n = 0x1 & (val>>7)
  @s += 1
  inc_pc_by_mode(mode)
end

#rol(arg, mode) ⇒ Object

rotate left



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# File 'lib/r6502/cpu_instructions.rb', line 181

def rol(arg, mode)
  case mode
  when :acc
    c = @c
    @c = (@a&0x80)>>7
    @a = 0xff & (@a<<1) | c
    @z = @a.zero? ? 1 : 0
    @n = (@a&0x80)>>7
  else
    val = @mem.get(arg)
    c = @c
    @c = (val&0x80)>>7
    r = 0xff & (val<<1) | c
    @z = r.zero? ? 1 : 0
    @n = (r&0x80)>>7
    @mem.set(arg, r)
  end
  inc_pc_by_mode(mode)
end

#ror(arg, mode) ⇒ Object

rotate right



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# File 'lib/r6502/cpu_instructions.rb', line 201

def ror(arg, mode)
  case mode
  when :acc
    c = @c
    @c = @a&0x01
    @a = (@a>>1) | (c<<7)
    @z = @a.zero? ? 1 : 0
    @n = (@a&0x80)>>7
  else
    val = @mem.get(arg)
    c = @c
    @c = val&0x01
    r = (val>>1) | (c<<7)
    @mem.set(arg, r)
    @z = r.zero? ? 1 : 0
    @n = (r&0x80)>>7
  end
  inc_pc_by_mode(mode)
end

#rti(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 477

def rti( arg, mode )
  flags = @mem.get(0x0100 + @s + 1)
  @s += 1

  @c = 0x1 & flags
  @z = 0x1 & (flags>>1)
  @i = 0x1 & (flags>>2)
  @d = 0x1 & (flags>>3)
  @b = 0x1 & (flags>>4)
  # bit 5
  @v = 0x1 & (flags>>6)
  @n = 0x1 & (flags>>7)

  hi = @mem.get(0x0100 + @s + 1)
  @s += 1
  lo = @mem.get(0x0100 + @s + 1)
  @s += 1
  @pc = 0xffff&((hi<<8) + lo)
end

#rts(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 503

def rts( arg, mode )
  lo = @mem.get(0x0100 + @s + 1)
  @s += 1
  hi = @mem.get(0x0100 + @s + 1)
  @s += 1
  @pc = 0xffff&((hi<<8) + lo + 1)
end

#sbc(arg, mode) ⇒ Object

subtract with carry



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# File 'lib/r6502/cpu_instructions.rb', line 27

def sbc(arg, mode)
  x = @a
  y = mode == :imm ? arg : @mem.get(arg)
  if @d == 0 #normal binary mode
    y = (y^0xff)
    r = x + y + @c
    @a = 0xff & r
    @v = (((0x7f&x) + (0x7f&y) + @c)>>7) ^ ((x + y + @c)>>8)
    @z = (0xff&r).zero? ? 1 : 0
    @c = r > 255 ? 1 : 0
    @n = (0x80&r)>>7
  else #BCD mode
    ones = (0xf&x) - (0xf&y)
    tens = ((0xf0&x)>>4) - ((0xf0&y)>>4)
    r0 = ones + 10*tens - (1 - @c)
    @c = r0 >= 0 ? 1 : 0
    r = r0 % 100
    @z = r.zero? ? 1 : 0
    @a = r + 6*((r/10).floor)
    @n = (0x80&@a)>>7
  end
  inc_pc_by_mode(mode)
end

#sec(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 224

def sec(arg, mode)
  @c = 1
  inc_pc_by_mode(mode)
end

#sed(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 228

def sed(arg, mode)
  @d = 1
  inc_pc_by_mode(mode)
end

#sei(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 232

def sei(arg, mode)
  @i = 1
  inc_pc_by_mode(mode)
end

#sta(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 411

def sta(arg, mode)
  @mem.set( arg, @a )
  inc_pc_by_mode(mode)
end

#step ⇒ Object 



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# File 'lib/r6502/cpu_execution.rb', line 20

def step
  instr, mode = instr_mode( mem.get(pc) )
  arg = decode_arg( mode, mem.get(pc+1), mem.get(pc+2) )

  puts "instr: #{instr} at pc 0x#{pc.to_s(16)} with arg #{arg.to_i.to_s(16)}"
  method( instr ).call( arg, mode )
  puts " a: #{a.to_s(16)} x: #{x.to_s(16)} y: #{y.to_s(16)} z: #{z.to_s(16)} n: #{n.to_s(16)} c: #{c.to_s(16)}"
  puts "==="
end

#stx(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 415

def stx(arg, mode)
  @mem.set( arg, @x )
  inc_pc_by_mode(mode)
end

#sty(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 419

def sty(arg, mode)
  @mem.set( arg, @y )
  inc_pc_by_mode(mode)
end

#tax(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 423

def tax(arg, mode)
  @x = @a
  @z = @x.zero? ? 1 : 0
  @n = (0x80&@x)>>7
  inc_pc_by_mode(mode)
end

#tay(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 429

def tay(arg, mode)
  @y = @a
  @z = @y.zero? ? 1 : 0
  @n = (0x80&@y)>>7
  inc_pc_by_mode(mode)
end

#tsx(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 435

def tsx(arg, mode)
  @x = @s
  @z = @x.zero? ? 1 : 0
  @n = (0x80&@x)>>7
  inc_pc_by_mode(mode)
end

#txa(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 441

def txa(arg, mode)
  @a = @x
  @z = @a.zero? ? 1 : 0
  @n = (0x80&@a)>>7
  inc_pc_by_mode(mode)
end

#txs(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 447

def txs(arg, mode)
  @s = @x
  inc_pc_by_mode(mode)
end

#tya(arg, mode) ⇒ Object 



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# File 'lib/r6502/cpu_instructions.rb', line 451

def tya(arg, mode)
  @a = @y
  @z = @a.zero? ? 1 : 0
  @n = (0x80&@a)>>7
  inc_pc_by_mode(mode)
end